Stretch wraps have been used widely in household and institutional packaging applications. The usage of stretch wrap, now made almost exclusively from LLDPE (Linear Low Density Polyethylene), is growing; the worldwide consumption for stretch wrap was well over 1 billion lbs. in 1991.
It is important for stretch wrap films to adhere to the objects and to each other during overwrapping. To achieve this, the film may be made of a polymer composition which has the desired properties, for example, copolymers of ethylene and vinyl acetate or vinyl chloride. With films made from LLDPE polymers a cling additive such as PIB (polyisobutylene) or amorphous atactic polypropylene, is usually incorporated into the film material; this additive migrates to the surface of the film where it modifies the film properties to achieve the desired overwrap characteristics. Quantitatively, the requisite degree of cling may be measured by the test procedure set out in ASTM D903-49 "Test for Peel Strength of Adhesives". Flexible films having a cling strength from 0.15 to 0.4 cm.-g. are generally considered to possess adequate cling, while values between 0.2 and 0.3 cm.-g. are normally considered to represent superior cling characteristics. Other important properties include elasticity, clarity, and stretchability and strength to withstand high speed wrapping.
Stretch wrap films may be either one-layer films or, more preferably, two or three-layer laminated materials produced by co-extrusion. Co-extruded films may have differing properties on the two sides, for example, to maximize the cling characteristics on the inside of the wrapped package while minimizing the degree of cling to other wrapped packages. A co-extruded stretch wrap film of this kind with a high degree of cling on one side and a sliding characteristic on the other is described in U.S. Pat. No. 4,518,654 (Eichbauer). Another film of this type is described in U.S. Pat. No. 4,820,589 (Dobreski), this film having an additive such as a polyamide or a poly-fluoro-olefin to reduce the cling characteristics on one side of the film. Another one-sided Cling stretch wrap film is described in U.S. Pat. No. 4,963,388 (Benoit).
U.S. Pat. No. 4,399,180 describes an improved type of stretch wrap film in which a primary layer of LLDPE is coextruded with a layer on one or both sides of a highly branched low-density polyethylene made in a free-radical polymerization process. As described in the patent, these films offer improved resistance to tear in both the machine and transverse directions as well as improved toughness and elongation characteristics. U.S. Pat. No. 4,418,114 (Briggs) describes similar types of film in the form of three-layer laminates and U.S. Pat. No. 5,019,315 (Wilson) describes another coextruded three-layer stretch wrap film fabricated from a high density polyethylene core layer and LLDPE outer layers.
Reprocessing stretch wrap waste back into the original products causes deterioration in the properties of the film products, especially in the optical quality, stretchability and strength of the films. For this reason, stretch wrap film is not normally recycled to product of the same type. On the other hand, recycling stretch wrap waste for bag applications is limited because the tackifiers, such as PIB, tend to cause the bags to block. Thus, stretch wrap film is not readily recycled into bag type film nor into films for other applications where it might otherwise have potential, for example, liners and food applications. The problem is particularly troublesome with bag films because the blocking characteristic impedes the separation of the film layers and the opening of the bag.